Building on the authors proven experience with (1) predictive scoring methods to predict massive transfusion, (2) creation and maturation of a massive transfusion protocol, and (3) design of large, multi-institutional studies, the PROMMTT investigators will conduct a prospective cohort study of severely injured patients (major trauma activations) arriving to three ACS-verified academic Level 1 Trauma Centers, in which the following 3 aims will be addressed: